Room temperature setting adhesive



United States Patent Ofice 2,859,200 Patented Nov. 4, 1958 ROOMTEMPERATURE SETTING'ADHESIVE Risto P. 'Lappala, Madison, Wis assignortoBjorksten Research Laboratories, Inc, Madison, Wis., a corporation ofIllinois a No Drawing. Application September 3, 1953 Serial N0. 378,425

3 Claims. Cl. 260-455) This invention relates to an organic adhesiveadapted to adhere metals to one another and to be applied and cured atroom temperatures andmore particularly to such adhesive comprisingacrylic resins.

The use of organic adhesives for bonding metal joints in aircraftconstruction instead of riveting or welding offers the advantagesof'lighter weight, smoother skin surfaces, and ease of application with.less complicated equipment. The use of adhesives in place of rivets insecuring together lightweight sheets of aluminum also has otheradvantages: Difficult assemblies, which are not possible with rivets,can be constructed; and perhaps most important, the fatigue strength ofadhesively bonded joints is generally at least 2 /2 times as great as acomparable riveted joint between thin sheets ofaluminum. It may readilybe seen that for modern aircraft applications, such an improvement infatigue strength of joints is of the utmost importance.

Adhesives based on phenolic resin-rubber blends have been successfullyused in manufacturing operations but require heat and pressure duringtheprocess. An adhesive which provides a secure bond between metalsheets at room temperature, with only slight pressure such as may beprovided by theweight of one sheet lying upon another, or by the use ofhand clamps or sandbags or the like can speed up manufacturing immenselyas well as making possible rapid repair work in the field where there isan absence of equipment adapted to provide heat and pressure.

A desirable adhesive, in addition to being adapted to provide a securebond at room temperature, should also retain its strengthat elevatedtemperatures andat extremely low temperatures. Furthermore it isdesirable that the adhesive should have attained at 1east'75% of itsultimate strength within 24' hours after first being applied and that itshould reachits ultimate strength in about days'at the most.

I have found that it is possible to provide a desirable adhesive of thetype described by utilizing a solution of polymethyl methacrylate in acopolymerizable mixture of one or more of the lower esters of acrylic ormethacrylic acid together with one or more unsaturated acids containingfrom 3 to 5 carbon atoms and containing one unsaturation, that is onedouble bond between carbon atoms.

It is therefore an object of this invention to provide an improvedadhesive for bonding together sheets of metal.

Another object is an adhesive for bonding together sheets of such metalsas aluminum which will provide a joint of great strength under onlyslight pressure at room temperature.

Another object is an adhesive for metals such as aluminum whichcomprises a copolymer of an acrylic ester and an unsaturated acid of lowmolecular weight.

Another object is an adhesively bonded joint of great strength betweenmetal surfaces. I

Further objects will become apparent from the following detaileddescription in which it is my intention to describe the invention andtoillustrate the wide'scope of its applicability.

This invention is an improvement in the adhesive disclosed and claimedin copending application Serial No. 326,787, filed'December 18, 1952,now abandoned, by Johan Bjorksten, Risto P. Lappala and Luther L.Yaeger.

In accordance with a preferred embodiment of my invention I may firstprepare a solution of about 4 to 10 parts of methylmethacrylate, about 1part methacrylic acid and about 2 to 5 parts polymethyl methacrylate.This mixture is then applied directly to the cleaned surfaces of each oftwo plates of aluminum which I may desire to bond together, after addingone or more catalysts immediately prior to such application. Thesurfaces to which the adhesive has been applied are then laid in contactwith one another and the assembly is allowed to standat room temperaturefor 24 hours. After about 5 hours the assembly may be freely handled andafter about 24 hours the joint is strong and rigid and has a strength ofas much' as 100% of the strength which it has after 5 days or 10 days.

The following examples illustrate the invention in greater detail.

Example 1 10 grams methacrylic acid inhibitorfree grams methylmethacrylate inhibitor free 30 grams polymethyl methacrylate moldinggranules (V Plexiglas, Rohm & Haas).

The above ingredients were heated at between F. and F. with an infra-redlamp with stirring until the polymethyl methacrylate was dissolved.

The mixture was then used as an adhesive for bonding together aluminumplates by adding to 24 grams of the adhesive, as catalysts, in sequence,5 drops of diethyl aniline, 10 drops of ethyl methyl ketone peroxidesold commercially as Lupersol DDM and 3 drops of a solution of cobaltnaphthenate containing 6% cobalt as metal,

in a su'itable solvent such as mineral spirits. The mixture thusprepared had a pot life of 30 minutes. mixture was used to bond togetheraluminum plates having a thickness of 0.064" in a lap joint /2 inch inwidth. A l-inch wide strip cut from such an assembly, normal to thejoint, was tested and it was found that the shear strength of the bondat room temperature was 4,400 pounds per square inch, at F. it was 3,600

Example 2 10 grams methacrylic acid (containing 0.1% hydroquinone aspolymerization inhibitor) 90 grams methyl methacrylate, inhibitor free-25 grams polymethyl methacrylate molding granules (V-100 Plexiglas, Rohm& Haas) The ingredients were mixed and utilized as an adhesive in themanner described in connection with Example 1. A joint between a pair ofaluminum plates bonded together with this adhesive exhibited properties'coni'par able to those of the joint described in Example l Thecatalyzed Example 3 10 grams methacrylic acid (containing 0.1%hydroquinone as polymerization inhibitor) 7 90 grams methyl methacrylate(containing 0.1% hydroquinone as polymerization inhibitor) 25' gramspolymethyl methacrylate molding powder (V-100 Plexiglas, Rohm & Haas)The ingredients were mixed and utilized as an adhesive in the mannerdescribed in connection with Example 1. A joint between a pair ofaluminum plates bonded together with this adhesive exhibited propertiescomparable to those of the joint described in Example 1.

Example '4 The ingredients were mixed and utilized as an ad hesive inthe manner described in connection with Example 1. A joint between apair of aluminum plates bonded together with this adhesive exhibitedproperties only slightly lower than those of the joint described inExample 1.

Example 5 grams methacrylic acid (containing 0.1% hydroquinone aspolymerization inhibitor)- 5 grams acrylic acid (containing 0.1%hydroquinone as polymerization inhibitor) 80 grams polymethylmethacrylate (containing 0.1% hydroquinone as polymerization inhibitor)30 grams polymethyl methacrylate molding granules (V-lOO Plexiglas, Rohm& Haas) The ingredients were mixed and utilized as an adhesive in themanner described in connection with Example 1. A joint between a pair ofaluminum plates bonded together with this adhesive exhibited propertiesonly slightly less desirable than those of the joint described inExample 1.

Example 6 grams methacrylic acid (containing 0.1% hydroquinone aspolymerization inhibitor) 80 grams methyl methacrylate (containing 0.1%hydroquinone as polymerization inhibitor) 35 grams polymethylmethacrylate molding granules (V-lOO Plexiglas, Rohm & Haas) Theingredients were mixed and utilized as an adhesive in the mannerdescribed in connection with Example l. A joint between a pair ofaluminum plates bonded together with this adhesive exhibited propertiesof satisfactory magnitude but lower than those of the joint described inExample 1.

- Example 7 5 grams methacrylic acid (containing 0.1% hydroquinone aspolymerization inhibitor) 95 grams methyl methacrylate (containing 0.1%hydroquinone as polymerization inhibitor) 20 grams polymethylmethacrylate molding granules (V-lOO Plexiglas, Rohm & Haas) proportionsof components from my adhesive and have shown certain compounds suitablefor inclusion therein they do not indicate the full useful range, forexample I may use from 5 to 20 parts of acid (methacrylic or acrylicacid or both), from 95 to 80 parts of methyl methacrylate, and from 10to 30 parts of polymethyl methacrylate molding granules, each of themonomers may be free of inhibitors or may contain hydroquinone as apolymerization inhibitor in the amount of .3% to .006%.

This invention represents a significant improvement over the inventiondisclosed in co-pending application Serial No. 326,787 for the reasonthat the compositions described herein can be prepared far moreeconomically due to the elimination of the heretoforecriticalprecopolymerization step and also due to the elimination of thenecessity for removing polymerization inhibitor from the monomersdescribed in that application. According to the instant invention theadhesive composition may be prepared merely by the mixing of theingredients and the application of moderate heat and stirring.

It will thus be apparent that the instant invention. relates to anadhesive between metal surfaces and for use between metal surfacescomprising a mixture of a monomer having the formula:

R O RC=(!7C// 0R1 wherein R is -H or CH and R is C,H and x is 1 or 2,and a monomer having the formula:

R RC=(|)C III wherein R is H or CH together with a polymer formed from amonomer having the first mentioned formula such as polymethylmethacrylate, wherein either of the above described monomers may containa small amount of hydroquinone or other polymerization inhibitors. Theinstant invention also relates to a preferred simple economical methodof preparing such adhesive.

Although the examples have shown onlyth'e use of polymethyl methacrylateas a polymer formed froma monomer having the first formula (being apolymer of a lower aliphatic ester of acrylic, methacrylic or crotonicacid), I have also used successfully other such .esters including:polyethyl methacrylate, polymethyl acrylate, polyethyl acrylate,polybutyl methacrylate, polylsobutylmethacrylate, polybutyl acrylate andI may also suitably use other such esters including: polyethylcrotonate, polymethyl crotonate, polybutyl crotonate, polycyclohexylacrylate, polycyclohexyl methacrylate, polyamyl acrylate, polyamylmethacrylate, polycyclohexyl crotonate, and the like.

It was found that when the concentration of the acid was greater than20%, the formation of insoluble particles in the hottest areas of thereaction flask was excessive, It was also observed that the strengths ofthe bonds produced with adhesives comprising more than 20%. of acid wereundesirably low. It was found preferable to use a concentration of atleast 5% of acid.

G enerally it has been found necessary to provide a min mum period ofabout 15 minutes for catalytic copolymerization to take place in thejoint before it may be handled without failure and, although longerperiods are necessary in some cases, 3 hours has been found sufli c 'entwith some compositions to complete the polymerizatlon sufficiently toobtain of the ultimate strength in the joint. During this period of 3hours or longer, the joint must not of course be subjected to forcessufficient to disturb the desired relation of the articles being adheredIt may thus be seen that the invention is broad in scope and should beinterpreted as including all equivalents which will be apparent to thoseskilled in the art and is to be limited only by the claims.

Having thus disclosed my invention, I claim:

1. A composition comprising 80 to 95 parts of at least one monomerselected from the group having the formula:

wherein R is a member from the group consisting of H and CH3.

2. A composition comprising 80 to 95 parts of at least one monomerselected from the group having the formula:

wherein R is a member from the group consisting of H and CH and R is C Hand x is a whole number not exceeding 2, to 30 parts of at least onepolymer formed from a monomer having said formula and 5 to 20 parts ofat least one monomer selected from the group having the formula:

wherein R is a member from the group consisting of -H and CH whereinsaid monomers contain .3 to .006% polymerization inhibitor. 7

3. A composition comprising to parts of at least one monomer selectedfrom the group having the formula:

wherein R is a member from the group consisting of --H and CH and R is CH and x is a whole number not exceeding 2, 10 to 30 parts of at leastone polymer formed from a monomer having said formula and 5 to 20 partsof at least one monomer selected from the group having the formula:

RC=OO/ wherein R is a member from the group consisting of H and CHwherein said monomers contain .3 to .006% hydroquinone.

References Cited in the file of this patent UNITED STATES PATENTS2,104,760 Renfrew Jan. 11, 1938, 2,273,891 Pollack et al. Feb. 24, 19422,373,488 Marks Apr. 10, 1945 2,464,826 Neher et a1 Mar. 22, 1949 OTHERREFERENCES Monomers,- by Blout et al., Methyl Methacrylate, pages 8 and9, published by Interscience Publishers, Inc., New York, N. Y.,copyright 1949.

1. A COMPOSITION COMPRISING 80 TO 95 PARTS OF AT LEAST ONE MONOMERSELECTED FROM THE GROUP HAVING THE FORMULA: